[PATCH] acpi: acpica: fix acpi operand cache leak in nseval.c

[Seunghun Han <kkamagui@gmail.com>]

I found an ACPI cache leak in ACPI early termination and boot continuing case.

When early termination occurs due to malicious ACPI table, Linux kernel
terminates ACPI function and continues to boot process. While kernel terminates
ACPI function, kmem_cache_destroy() reports Acpi-Operand cache leak.

Boot log of ACPI operand cache leak is as follows:
>[    0.464168] ACPI: Added _OSI(Module Device)
>[    0.467022] ACPI: Added _OSI(Processor Device)
>[    0.469376] ACPI: Added _OSI(3.0 _SCP Extensions)
>[    0.471647] ACPI: Added _OSI(Processor Aggregator Device)
>[    0.477997] ACPI Error: Null stack entry at ffff880215c0aad8 (20170303/exresop-174)
>[    0.482706] ACPI Exception: AE_AML_INTERNAL, While resolving operands for [OpcodeName unavailable] (20170303/dswexec-461)
>[    0.487503] ACPI Error: Method parse/execution failed [\DBG] (Node ffff88021710ab40), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.492136] ACPI Error: Method parse/execution failed [\_SB._INI] (Node ffff88021710a618), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.497683] ACPI: Interpreter enabled
>[    0.499385] ACPI: (supports S0)
>[    0.501151] ACPI: Using IOAPIC for interrupt routing
>[    0.503342] ACPI Error: Null stack entry at ffff880215c0aad8 (20170303/exresop-174)
>[    0.506522] ACPI Exception: AE_AML_INTERNAL, While resolving operands for [OpcodeName unavailable] (20170303/dswexec-461)
>[    0.510463] ACPI Error: Method parse/execution failed [\DBG] (Node ffff88021710ab40), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.514477] ACPI Error: Method parse/execution failed [\_PIC] (Node ffff88021710ab18), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.518867] ACPI Exception: AE_AML_INTERNAL, Evaluating _PIC (20170303/bus-991)
>[    0.522384] kmem_cache_destroy Acpi-Operand: Slab cache still has objects
>[    0.524597] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc5 #26
>[    0.526795] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>[    0.529668] Call Trace:
>[    0.530811]  ? dump_stack+0x5c/0x81
>[    0.532240]  ? kmem_cache_destroy+0x1aa/0x1c0
>[    0.533905]  ? acpi_os_delete_cache+0xa/0x10
>[    0.535497]  ? acpi_ut_delete_caches+0x3f/0x7b
>[    0.537237]  ? acpi_terminate+0xa/0x14
>[    0.538701]  ? acpi_init+0x2af/0x34f
>[    0.540008]  ? acpi_sleep_proc_init+0x27/0x27
>[    0.541593]  ? do_one_initcall+0x4e/0x1a0
>[    0.543008]  ? kernel_init_freeable+0x19e/0x21f
>[    0.546202]  ? rest_init+0x80/0x80
>[    0.547513]  ? kernel_init+0xa/0x100
>[    0.548817]  ? ret_from_fork+0x25/0x30
>[    0.550587] vgaarb: loaded
>[    0.551716] EDAC MC: Ver: 3.0.0
>[    0.553744] PCI: Probing PCI hardware
>[    0.555038] PCI host bridge to bus 0000:00
> ... Continue to boot and log is omitted ...

I analyzed this memory leak in detail and found acpi_ns_evaluate() function
only removes info->return_object in AE_CTRL_RETURN_VALUE case. But, when errors
occur, the status value is not AE_CTRL_RETURN_VALUE, and info->return_object is
also not null. Therefore, this causes acpi operand memory leak.

This cache leak causes a security threat because an old kernel (<= 4.9) shows
memory locations of kernel functions in stack dump. Some malicious users
could use this information to neutralize kernel ASLR.

I made a patch to fix ACPI operand cache leak.

Signed-off-by: Seunghun Han <kkamagui@gmail.com>
---
 drivers/acpi/acpica/nseval.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/acpica/nseval.c b/drivers/acpi/acpica/nseval.c
index d22167c..f13d3cf 100644
--- a/drivers/acpi/acpica/nseval.c
+++ b/drivers/acpi/acpica/nseval.c
@@ -308,6 +308,14 @@ acpi_status acpi_ns_evaluate(struct acpi_evaluate_info *info)
 		/* Map AE_CTRL_RETURN_VALUE to AE_OK, we are done with it */
 
 		status = AE_OK;
+	} else if (ACPI_FAILURE(status)) {
+
+		/* If return_object exists, delete it */
+
+		if (info->return_object) {
+			acpi_ut_remove_reference(info->return_object);
+			info->return_object = NULL;
+		}
 	}
 
 	ACPI_DEBUG_PRINT((ACPI_DB_NAMES,
-- 
2.1.4